In applications where sliding contact occurs between the tribological surfaces of two machine components, such as in plain bearing arrangements and dynamic sealing arrangements, friction and heat are necessarily generated. This can lead to fretting and wear and accelerated failure of a component of the bearing arrangement or sealing arrangement. One way of reducing friction is to lubricate the tribological surfaces with an oil or grease, such that an oil film develops therebetween. A disadvantage of such lubrication is the fact that the oil film is not present upon start-up and that formation of the lubricating layer only occurs when a particular temperature has been reached.
Therefore, in addition to or instead of using a lubricant, it can be beneficial to apply a low-friction coating to the tribological surface of a machine component that is in sliding contact with another surface. An example of a bushing assembly comprising an anti-friction layer is disclosed in U.S. Pat. No. 6,139,261. The bushing assembly supports a torque shaft relative to a housing and provides a bushing mounted to the housing and a wear sleeve mounted to the shaft. A radially inner surface of the bushing is provided with a PTFE coating of 10-20 mm thickness.
It is also known to use low-friction coatings in dynamic sealing applications, for example, from EP1106878. A seal for a rolling element bearing is described, which has an elastomeric sealing element comprising a contact lip that bears against a counterface on an inner ring of the bearing. A sealing surface of the lip is provided with a PFTE coating having a thickness of less than 0.2 mm.
PTFE has excellent low-friction properties, but is a soft material and can be difficult to apply in a durable manner.
It would be an advantageous object of the invention to provide a machine component which displays low friction when in sliding contact with a counter surface of another machine component, by means of a coating that mitigates at least some of the disadvantages associated with prior-art solutions.